Electrical apparatus



o 4 L. H. BEDFORD ET-AL 2,387,110

ELECTRICAL APPARATUS Original Filed May 8. 19:59

LESLIE HEIRBERT .BEDFORD LI ONEL JOFEH WJRL'IER HENRY STEVENS PatentedOct. 16, 1945 ELECTRICAL APPARATUS Leslie Herbert Bedford, Lionel Jofehand Walter Henry Stevens, London, England, assignors to A. C. CossorLimited, London, England, a

British company Original application May 8, 1939, Serial No.

272,508. Divided and this application September 19, 1942, Serial No.459,018.

Britain May 10, 1938 6 Claims.

The invention relates to an electromagnetic system for the deflection ofthe electron beam of a cathode ray tube in two mutually perpendiculardirections.

The present application is a division of our prior application SerialNo. 272,508, filed May 8, 1939, now Patent No. 2,336,837.

An object of the invention is to provide a robust and compact assemblyof deflection coils for the two directions of deflection.

A further object is to minimize mutual interference between the currentspassed through the deflection coils and mutual interference between theelectromagnetic deflection fields produced thereby.

A preferred arrangement embodying the invention is illustrated in theaccompanying drawing, in which Figure 1 shows a perspective View of anelectromagnetic deflecting apparatus surrounding the neck of a cathoderay tube suitable for a television receiver and Figure 2 is adiagrammatic sectional view of Figure 1 taken on the plane of thecentral lamination II.

The electron gun (which includes the cathode) and the fluorescent screenare not shown, but the former is assumed to be situated below, and thelatter above, the assembly shown, so that the electron beam passesupward through the neck I of the cathode ray tube.

The two coils I produce one of the electromagnetic deflection fields andthe coils 8 produce the other. Each of these fields is of the kindcomprising a central flux path passing transversely through the neck ofthe tube and comprising two symmetrical side paths passing on mutuallyopposite sides of the neck of the tube.

The coil l are bent around to lie in Contact with the former 6 which isa sleeve of insulating material closely surrounding the neck of thetube. The central fiux path of the field of the coils 1 passes throughthe neck of the tube in the direction of the common axis 1' of the coilsi, see Figure 2.

The coils 8 have their centres substantially on the common axis 1 of thecoils l, but their own axes are perpendicular to the axis of the coilsl. The central flux path of the field of the coils 8 passes through theneck of the tube in the direction 8 parallel-to the axes of the coils 8,see Figure 2. I I

The part of the magnetic circuit of the coils 8 external to the tube isformed by laminations H in the form of complete rectangles offerromagnetic materials. These laminations are spaced apart by woodenspacers l2.

In Great The part of the magnetic circuit of the coils external to thetube is formed by laminations ea, 9c of ferromagnetic material. Theseare divided, the part 9a, in the form of a complete rectangle, beingplaced on the end of the assembly nearer the fluorescent screen, and theother part 90, forming substantially a rectangle, being placed on theend of the assembly nearer the cathode. The part 9b, 9c is subdividedinto two U-shaped parts by the provision of gaps in the region of theends of the central flux path of the magnetic circuit belonging to thecoils 1. These gaps minimize the short-circuiting of the magneticcircuit of the coils 8. The laminations 9a, 9b, 9c, are spaced from thetwo outer laminations H by wooden spacers l0, and are thus arranged atthe ends of the coils 1.

From Figure 2 it will be seen that the central fillX path for coils l isdirected along the axis 1 of these coils, while the central flux pathfor the coils 8 is directed along the axi 8 parallel to the axes ofthese coils but at right angles to the axis l. The flux from the centralpath along axis 1 divides, and a portion represented by the link ofdotted arrows la forms one side path for this magnetic circuit and theother portion represented by the link of dotted arrows 11) forms theother side path for thi circuit, these side paths being completed partlythrough lamination 9a. In a like manner, the flux from the central pathalong axis 8 divides, a portion going through one coil 8 surrounding oneleg of lamination II and the other portion going through the other coil8 surrounding the opposite leg of the lamination.

By virtue of the arrangement of the coils 8 in relation to the coils l,the electromagnetic pickup of the coils 8 resulting from current changesin the coils l is neutralized. This is due to the fact that coils isurround the central flux path of one deflecting magnetic circuitwhereas coil 8 are linked separately with the side paths only of theother deflecting magnetic circuit. The coils 8 may be arranged foradjustment in the direction of their axes so as to provide for accurateadjustment of this neutralisation.

The coils 8 should preferably be enclosed in electrostatic screens tominimise electrostatic interference between the two pairs of coils.

The coils I should preferably be so electrically connected in thercircuit as to be operated in respect to alternating current,symmetrically'about earth. This is diagrammatically indicated in thedrawing by showing the terminals (3 of the circuit for coils 1 connectedby leads one to each coil, and by showing the other leads from each coilconnected together and earthed at Hi.

When the deflection system shown and described is used for televisionscanning, the coils 8 are employed to produce the lower frequency orframe deflection and the coils to produce higher frequency or linedeflection. The laminations 8 are preferably then made of Rhometal andthe laminations H of Stalloy.

The ratio of permeability at line frequency to permeability at framefrequency is substantially higher for Rhometal than for Stalloy.

It will be understood that features of this invention are applicable notonly to cathode ray tubes having fluorescent screens but also to othertypes such as iconoscopes and electron beam defiection valves. We claim:

1. In a cathode ray tube having a compact electromagnetic deflectionsystem including magnetic circuits for controlling the electron beam intwo mutually perpendicular directions of deflection, each of whichcomprises a central flux path passing through the tube and two sidepaths for the flux which pass on mutually opposite sides of the tube,the combination of coils for producing the flux to control thedeflection in one direction positioned about a common axis and onopposite sides of the tube about the central flux path of a firstmagnetic circuit, and coils for producing the flux to control thedeflection in a perpendicular direction positioned on side flux paths ofa second magnetic circuit with their centres substantially on saidcommon axis at opposite sides of the tube and with their axesperpendicular to said common axis.

2. In a cathode ray tube having a compact electromagnetic deflectionsystem including magnetic circuits for controlling the electron beam intwo mutually perpendicular directions of deflection, each of whichcomprises a central flux path passing through the tube and two sidepaths for the flux which pass on mutually opposite sides of the tube,the combination of coils for producing the flux to control thedeflection in one direction positioned about a common aXis and onopposite sides of the tube about the central flux path of a firstmagnetic circuit, and coils for producing the flux tocontrol thedeflection in a perpendicular direction positioned on side flux paths ofa second magnetic circuit with their centres substantially on saidcommon axis at opposite sides of the tube and with their axesperpendicular to said common axis, the coils'for producingelectromagnetic flux in said second magnetic system being moveablysupported for adjustment in the direction of their axes.

3. In a cathode'ray'tube' having a compact electromagnetic deflectionsystem including magnetic circuits for controlling the electron beam intwo mutually perpendicular directions of deflection, each of whichcomprises a central flux path passing through the tube and two sidepaths for the flux which pass on mutually opposite sides of the tube,the combination of coils for producing the flux to control thedeflection in one direction positioned about a common axis and onopposite sides of the tube about the central flux path of a firstmagnetic circuit, means for maintaining the electrical central point ofsaid coils at a constant potential, and coils for producing the flux tocontrol the deflection in a perpendicular direction positioned on sideflux paths of a second magnetic circuit with their centres substantiallyon said common axis at opposite sides of the tube and with their axesperpendicular to said common axis.

4. In a cathode ray tube having a compact electromagnetic deflectionsystem including magnetic circuits for controlling the electron beam intwo mutually perpendicular directions of deflection, each of whichcomprises a central flux path passing through the tube and two sidepaths for the flux which pass on mutually opposite sides of the-tube,the combination of coils for producing the flux to control thedeflection in one direction positionedabout'a common axis and onopposite sidesof the tube about the central flux path of a firstmagneticcircuit, means for grounding the centre point of said coils, and coilsfor producing the flux to control the deflection in a perpendiculardirection positioned on side flux paths of a second magnetic circuitwith their centres substantially on said common axis at opposite sidesof the tube and with their axes perpendicular to said common axis.

5. In a cathode raytube having a compact electromagnetic deflectionsystem including magnetic circuits for controlling the electron beam intwo mutually perpendicular directions of deflection, each of whichcomprises a central flux path passing through the tube and two sidepaths for the flux which pass on mutually opposite sides of the tube,the combination of coils for producing the flux to control thedeflection in one direction positioned about a common axis and onopposite sides of the tube about the central flux path of a firstmagnetic circuit, coils for producing the flux to control the deflectionin a perpendicular direction positioned on side flux paths of a secondmagnetic circuit with their centres substantially on said common axis atopposite sides of the tube and with their axes perpendicular to saidcommon axis, a ferromagnetic path for said second magnetic circuit, anda divided ferromagnetic path for said'first magnetic circuit, thedivided portions of which being oppositely displaced from the secondmagnetic circuit in the direction parallel to the electron beam path. 7

6. In a cathode ray tube having a compact electromagnetic deflectionsystem including magnetic circuits for controlling the electron beam intwo mutually perpendicular directions of deflection at substantiallydifierent'frequencies of fleld flux, each of which comprises a centralflux path passing through the tube and two ferro-magnetic paths externalof the tube for the flux which passes on mutually opposite sides of thetube, the combination of ferromagnetic means providing external pathsfor eachof said magnetic circuits, the external ferromagnetic paths ofthe magnetic circuit carrying the higher frequency of field flux havinga substantially greater ratio of permeability at high frequencies topermeability at low frequencies than have the external ferromagneticpaths of the magnetic circuit carrying the field flux of lowerfrequency.

} LESLIE HERBERT LIONEL JOFEH.

WALTER HENRY STEVENS.

BEDFORD.

